Different formulations applicable to agrochemicals vary according to purpose of the application, nature of the active ingredients, kind of other components like surfactants, adjuvants etc. Out of the many challenges that one has to overcome to come up with a better performing agrochemical composition, certain properties are critical in determining the performance. Rainfastness is one such property as most of the active ingredients tend to be washed off by rain.
A pesticide is considered rainfast, if it has been adsorbed/absorbed by plant surface so that it will still remain available after rainfall or irrigation. The degree of rainfastness of pesticides is highly variable and depends on the physico-chemical properties of the active ingredient. Rainfall can adversely affect a pesticide application by directly washing the pesticide away or physically removing it, or diluting the product to a less effective form. Redistribution of the active ingredient can also happen after a rainfall so that the active ingredient may remain less available.
Dithiocarbamates are the most widely used fungicides. Examples include mancopper, maneb, mancozeb, metiram, propineb and zineb.
J. Environ Sci Health B. 2007, 133-41 discloses a study on retention and rainfastness of mancozeb as affected by physicochemical characteristics of adaxial apple leaf surface after enhanced UV-B radiation.
The rain fastness of dithiocarbamates in dry form is enhanced by formulation with nonionic water-soluble polymers such as hydroxyl (C2-C5) alkyl cellulose, polyethylene oxide, polyvinyl alcohol, polyvinyl pyrrolidone as disclosed in EP 0245970. However use of these high molecular weight polymers often causes severe formulation problems such low suspensibility and aggregation which in turn will result in degrading of the physical/chemical properties of the composition.
EP 0950354 discloses use of low molecular weight polyvinyl alcohol to improve the physical properties of dithiocarbamate based compositions.
All the prior arts described herein experience serious drawbacks especially while making the formulation. Use of high molecular weight polymers with dithiocarbamates usually leads to flocculation problems. Dry formulations face low suspensibility and aggregation while aqueous suspensions have gelation problems.
Therefore, there is a need for compositions comprising one or more active ingredients with increased rainfastness while maintaining the physico-chemical properties of the composition.
Surprisingly inventors of the present invention found out that a combination comprising pesticides such as dithiocarbamates and polycarboxylates impart increased rainfastness as well as improved performance.